🔧 Troubleshooting Bible: Zinc Alloy Rack Plating
Philosophy: Identify the root cause, fix it, and prevent it. Do not just "add more brightener."
Part I: Common Defects & Solutions
1. Blistering (The #1 Enemy)
Description: Small bubbles appear on the surface immediately after plating or after the Baking/Aging process.
Root Cause Analysis:
Cause A: Poor Degreasing. Oil remains in the logo or crevices.
Cause B: Over-Etching. The Acid Activation was too long or used HCl, attacking the Zinc surface.
Cause C: Immersion Copper. The parts entered the Cyanide Copper tank without current, causing a loose copper layer to form.
The Master's Fix:
Water Break Test: Dip a cleaned rack in water. If water beads up, dump the Degreasing tank.
Check Acid: Switch to [QLQ Product] Fluoride Activation Salt. Limit time to < 10 seconds.
Live Entry Check: Ensure the rectifier is ON (2-3 Volts) before the rack touches the Cyanide Copper solution.
2. Spring Fracture (Hydrogen Embrittlement)
Description: The stainless steel spring inside the zipper pull snaps when the user pulls it.
Root Cause Analysis:
Cause A: Use of Hydrochloric Acid (HCl) in pre-treatment.
Cause B: Plating Nickel too hard (Brittle).
Cause C: Delayed Baking. Waiting > 4 hours to put parts in the oven.
The Master's Fix:
Ban HCl: Remove all Hydrochloric Acid from the pre-treatment line.
Softener Boost: Increase [QLQ Product] Nickel Softener concentration by 20%.
SOP: Parts must go from the Drying Station $\rightarrow$ Oven within 1 hour. (180°C x 3 Hours).
3. Roughness / Pitting ("Sandpaper" Surface)
Description: Tiny granules or pinholes on the mirror surface.
Root Cause Analysis:
Cause A: Solid Particles. Broken anode bags or dirty filters.
Cause B: High Current. "Burning" the tips of the zipper pulls.
Cause C: Gas Trapping. Hydrogen bubbles sticking to the surface (Pitting).
The Master's Fix:
Filter Check: Change filter cores (5 micron).
Wetting Agent: Add [QLQ Product] Anti-Pit Wetting Agent to the Nickel/Acid Copper tank.
Agitation: Ensure the Cathode Rocker is moving smoothly to shake off bubbles.
4. Color Variation (Imitation Gold)
Description: Some racks are yellow, some are reddish.
Root Cause Analysis:
Cause A: Temperature Fluctuation. ±2°C difference changes the color.
Cause B: Current Density. High current = Redder; Low current = Yellower.
The Master's Fix:
Install a high-precision thermostat (±0.5°C).
Standardize the rack load (always 600 pcs/rack).
Part II: The Stripping (Re-work) Protocols
Warning: Stripping Zinc Alloy is risky. The base metal (Zinc) dissolves faster than the plating (Copper/Nickel). You must use Specialized Inhibited Strippers.
Scenario A: Stripping the Top Coat Only (Gold / Chrome / Gunmetal)
Situation: The base Nickel is good, but the Gold color is wrong. You want to strip the color and re-plate the color.
Process: Electrolytic or Immersion.
Formula (Chrome/Gunmetal Strip):
[Purchase Locally] Hydrochloric Acid: 50%.
Process: Dip for 10-30 seconds. The color disappears, revealing the white Nickel.
Next Step: Reactivate in [QLQ Product] Nickel Activator $\rightarrow$ Re-plate Color.
Formula (Imitation Gold Strip):
[QLQ Product] Gold Stripping Powder: 50 g/L.
Process: Anodic (+) Electrolysis.
Next Step: Rinse $\rightarrow$ Acid Dip $\rightarrow$ Re-plate Gold.
Scenario B: Stripping "Down to Base" (Removing Nickel & Copper)
Situation: The part has blisters or roughness. You must strip everything down to the raw Zinc Alloy casting.
The Challenge: You need to strip the Nickel/Copper without eating the Zinc zipper pull (which will cause it to lose dimension or become pitted).
Formula: Non-Cyanide Immersion Stripper (The Safe Way)
This is a slow but safe method specifically for Zinc Die-cast.
Tank: 304 Stainless Steel (Heated).
Chemicals:
[QLQ Product] Zinc-Base Nickel Stripper Salt: 250 g/L.
[Purchase Locally] Ethylenediamine (Complexer): 60 ml/L.
[QLQ Product] Stripping Accelerator: 10 ml/L.
Parameters:
Temp: 60°C – 70°C.
Time: 1 – 2 Hours (Depending on Nickel thickness).
Agitation: Mechanical movement required.
The "Stripping Cycle" SOP:
Clean: Degrease the bad parts first.
Strip: Immerse in the stripping tank until the grey Zinc surface appears.
Smut Removal: The parts will come out black/brown. Dip in [QLQ Product] Smut Remover or dilute Nitric Acid (1%) for 2 seconds.
Re-Polishing (Mandatory):
Critical: You cannot re-plate a stripped zinc part immediately. The surface has been chemically roughened.
Action: Send the parts back to the Polishing Department for "Buffing" (Touch-up) to restore the mirror shine.
Re-Plating: Treat as raw material.
Scenario C: Stripping the Rack Tips (Jig Maintenance)
Situation: The contact points of the Cage Rack get built up with thick metal.
Tank: Plastic (PVC).
Formula:
[Purchase Locally] Nitric Acid: 50%.
[Purchase Locally] Water: 50%.
Process: Dip the Empty Rack tips.
Warning: Violent Fumes! Must be done in a separate room with a Scrubber tower.
🌟 Expert Advice: The "Cost of Stripping"
To the Boss:
Stripping is expensive.
Cost 1: Chemical cost of stripper (High).
Cost 2: Labor to un-rack and re-polish.
Cost 3: Waste treatment (Stripping solution is loaded with heavy metals).
The Master's Rule:
"If the defect rate is < 5%, it is often cheaper to Scrap (Melt Down) the zinc parts than to strip them. Only strip high-value items or urgent orders where raw material is unavailable."